Virtual reality computer systems provide users with the illusion that they are part of a “virtual” environment and may be used for training and/or entertainment purposes. In many fields, virtual reality systems have been used successfully to allow a user to learn from and experience a realistic virtual environment. The appeal of using virtual reality computer systems for training relates, in part, to the ability of such systems to allow trainees the luxury of confidently operating in a highly realistic environment and making mistakes without real world consequences. For example, in the medical field, a virtual reality computer system allows a doctor-trainee or other human operator or user to manipulate an intravascular or laparoscopic tool within a computer-simulated body and thereby perform medical procedures on a virtual patient. In this instance, a user device such as a computer mouse or joystick is used to represent a surgical instrument. As the surgical instrument moves within a provided space or structure, results of such movement are updated and displayed in a body image displayed on the screen of the computer system so that the operator gains the experience of performing such a procedure without practicing on an actual human being or a cadaver. In other applications, virtual reality computer systems allow a user to handle and manipulate the controls of complicated and expensive vehicles, equipment, and other machinery.
For virtual reality systems to provide a realistic and therefore effective experience for the user, sensory feedback and manual interaction should be as natural as possible. In addition to sensing and tracking a user's manual activity and feeding such information to a controller or computer to provide a 3D visual representation to the user, a human interface mechanism should also provide tactile and/or kinesthetic feedback, more generally known as haptic feedback herein. The need for the user to obtain realistic haptic feedback is extensive in many kinds of simulations and other applications. For example, in medical/surgical simulations, the “feel” of a surgical tool is important as it is moved within the simulated body. It is invaluable to a medical trainee to learn how an instrument moves within a body, how much force is required depending on the operation performed, the space available in a body to manipulate an instrument, etc.
Many types of actuators for generating computer-controlled forces are known, including DC and stepper motors, voice coils, hydraulic actuators, and pneumatic actuators. Some devices are active, such as motors, which mean that the device provides an active force that has the ability to move an object or push back on the user. Other actuators are passive, such as brakes, which provide a resistance to motion generated by another source such as the user and cannot generate forces on their own. An advantage of active devices is their ability to simulate all kinds of force sensations. However, active actuators may be unstable and may settle into a feedback loop in which oscillating forces are output on the manipulandum, for example. Dampers may be utilized with an active actuator in order to stabilize the system, such as those described in “Initial results using Eddy Current Brakes as Fast Turn-on, Programmable Physical Dampers for Haptic Rendering” by Gianni Campion, Andrew Gosline, and Vincent Hayward, and “Eddy Current Brakes for Haptic Interfaces: Design, Identification, and Control” by Andrew Gosline and Vincent Hayward, both of which are herein incorporated by reference in their entirety. The above-mentioned articles describe the use of an eddy current brake as a linear, fast actuating, programmable viscous damper in order to stabilize a motor, which is utilized as the active actuator for haptic rendering. Other disadvantages of active actuators include a high cost, and large size and weight. Passive actuators, on the other hand, while not able to output all the types of force sensations of active actuators, can provide relatively high magnitude forces, are inherently stable and safe, and are typically of low cost and weight. However, standard passive actuators can still be expensive for lower-cost devices and can still add significant weight to an interface device. In addition, a passive actuator may be limited in its ability to simulate different types of force sensations. For example, the article “Passive Viscous Haptic Textures. Proc. 16th Symposium on Haptic Interfaces For Virtual Environment And Teleoperator Systems” by Gianni Campion, Andrew Gosline, and Vincent Hayward, herein incorporated by reference in its entirety, discusses the use of an eddy current brake to generate a viscous texture on a haptic interface. The eddy current brake is not utilized to simulate other force sensations such as vibrations, pulses, jolts, and the like.
With demand for haptic interfaces in areas such as medical training, manufacturing, and perception research, there is a demand for improved and/or alternative actuators for providing haptic effects.